Method for coating plastics onto a substrate employing a plasma



A ril 16, 1968 J. W. WINZELER ETAL METHOD FOR COATING PLASTICS ONTO ASUBSTRATE EMPLOYING A PLASMA Filed Dec. 20, 1962 m -4 wATER SOURCEPOWDER SOURCE 43 GAS Tom? SOURCE s SOURCE 46 47 52 INVENTOR. JOHN W.WINZELER BY JAMES F. TUCKER ATTQRNEY United States PatentContinuation-impart of application Ser. No. 126,402,

June 13, 1961. This application Dec. 20, 1962, Ser- No. 246,170

The portion of the term of the patent subsequent to Apr. 20, 1982, hasbeen disclaimed 3 Claims. (Cl. 117-93.1)

This invention relates to a method of applying plastic coatings to asubstrate. The present application is a continuation-in-part of ourco-pending patent application Ser. No. 126,402, now Patent No. 3,183,337filed June 13, 1961, for Electrical Plasma-Jet Spray Torch and Method.

An object of the present invention is to provide a method of sprayingvarious plastics by means of an electrical plasma-jet torch, therebymaking it simple, economical and commercially practical to plastic coatnumerous objects and substrates relative to which plastic coating wasnot previously possible and/or practical.

This and other objects and advantages of the invention will be morefully set forth in the following specification and claims, considered inconnection with the attached drawing to which they relate.

In the drawing:

' FIGURE 1 is a longitudinal central sectional view illustrating anelectrical plasma-jet spray torch adapted to effect plastic coating inaccordance with the present invention;

FIGURE 2 is a transverse section taken on line 2-2 of FIGURE 1; and

FIGURE 3 is a transverse section taken on line 3-3 of FIGURE 1.

Referring to the drawing, an electrical plasma-jet spray torch isillustrated to comprise a unitary casing and handle formed of a suitableinsulating plastic. The handle portion of element 10 is hollow and issufiiciently large to receive conduits leading from suitable sources ofcurrent, water, gas and spray material. The casing is provided with asuitable metal shield 11 between the plasma jet 12 and the handle, suchshield serving to protect from the intense heat of the plasma jet thehand of the operator holding the apparatus.

The apparatus further comprises an insulating body 13, preferably formedof a suitable plastic such as a phenolic, having a central flangeportion 14 the cylindrical outer wall of which abuts the interiorcylindrical wall of casing 10. Abutted against the forward surface offlange portion 14 is a front housing element 15 having a generallyannular shape. Such element may be formed of brass or other suitableelectrical conductor. Abutted against the rear surface of flange portion14 is the rim of a generally cup-shaped rear housing element 16 which isalso formed of brass or other suitable conductor.

A front electrode element 18, which is preferably formed of copper, hasits generally disc-shaped forward portion abutted sealingly againstfront housing element 15. The stem portion 19 of the front electrodeextends inwardly toward the rear housing element, having a flangedportion 20 which abuts the inner surface 21 of the phenolic body 13.Such inner surface 21 is cylindrical in shape and defines the outerportion of a vortex chamber 23 into which gas is introduced tangentiallyas will be stated hereinafter. The front portion of such vortex chamberis defined by stem 19, including its flange 20, Whereas the rear portionof the chamber is defined by a disc 24 formed of a suitable insulatingmaterial.

The vortex chamber 23 communicates with, and is coaxial with, a nozzlepassage 25 which is bored centrally through the nozzle electrode. Suchnozzle passage permits discharge of gas from the vortex chamber 23 tothe ambient atmosphere and in the form of the plasam jet 12, it beingunderstood that the temperature of the plasma jet depends upon severalfactors including the location and magnitude of an electric are 26 whichis maintained between the interior wall of nozzle passage 25 and the tipof a rear electrode assembly next to be described.

The rear electrode assembly comprises an externallythreaded adjustmentshaft or rod 28 formed of copper or other suitable conductor, such shaftor rod being threaded into an internally-threaded bore through a stemportion 29 of the rear housing element .16. Soldered coaxially at theextreme front end of the threaded shaft 28 is a rear electrode rod 30preferably formed of thoriated tungsten. The rod 30 has a diametersubstantially smaller than the nozzle passage 25 with which it iscoaxial, so that the vortically-flowing gas may pass forwardly fromchamber 23 to create the plasma jet 12. An insulating adjustment knob 31is non-rotatably connected through a rod 32 to the rear end of shaft 28,so that turning of the knob 31 operates through the shaft 28 to move thetip of electrode rod 30 either forwardly or rearwardly.

A lock knob 33, preferably formed of a suitable insulating plastic, isinternally threaded to mate with the outer end of adjustment shaft 28,and is also bored to slidably receive the rod 32. An inner or stemportion 34 of knob 33 extends slidably through casing 10 and abuts theouter surface of rear housing 16, The lock knob 33, when manuallyrotated after the electrode position has been adjusted, operates in themanner of a lock nut to prevent rotation of shaft 28. Furthermore, thelock nut jams the threads of elements 28 and 29 tightly against eachother to prevent arcing therebetween.

The stem portion 29 of the rear housing extends through a bore in body13, and also through a somewhat smaller opening in disc 24, to thevortex chamber 23. A counterbore 36 is provided around the stem 29,inwardly adjacent disc 24, and communicates .through passages 37 with acoolant chamber 38 which is defined by the interior surfaces of the rearhousing element 16 and by the rear radial surface of body 13. A secondcoolant chamber 39 is defined around the nozzle passage 25 by stem 19(including its flange 20), by the front edge or rim of body 13, and bythe interior surface of front housing 15. The main coolant chambers 38and 39 communicate with each other through a passage 41 which extendsthrough body 13 radially-outwardly of vortex chamber 213. The passages37 permit circulation of water from the rear coolant chamber 38 to theannulus formed by counterbore 36, so that the forward portion of stem 29is cooled.

Proceeding next to a description of the various supply sources, andassociated elements, a suitable source (or sources) of both current andwater is indicated schematically at 43. Such source is connected throughwater-conducting cables 44 and 45 (such as insulating plastic waterconduits containing large electrical conductors) to the front and rearhousing elements and 16, respectively. Water is thus fed from source 43to coolant chamber 39 in the front electrode, from which it flowsthrough passage 41 to rear coolant chamber 33 and the associatedcounterbore 36, after which it discharges through the cable to asuitable drain.

The electricity which passes through cables 44 and 45 can only flowbetween the electrodes in the form of the am 26, since the water whichflows through passage 41 has a high electrical resistance. Thus, theelectrical circuit comprises current and water source 43, cable 44,front housing element 15, front electrode 18, are 26, rear electrode rod30, adjustment shaft 28, rear housing element 16, and cable 45 back tosource 43. The current source is normally a D.C. source adapted todeliver very large currents at relatively low voltages. The polarity ofthe source is normally such that nozzle electrode 18 is positive, andrear electrode rod 30 is negative.

A suitable source 46 of gas under pressure is schematically indicated inFIGURE 1, being connected through a conduit 47 to a passage 48 (FIGURE2) which extends through body 13 and is tangential to the gas Vortexchamber 23. Gas is thus introduced from source 46 into the chamber,where it whirls at substantial velocity and then passes forwardlythrough nozzle passage 25 in a vertical or helical manner aroundelectrode rod 30.

The illustrated means for introducing spray material into the plasma jet12 comprises a plurality of sources 50 and 51 of powdered plastic. It isto be understood, however, that it is also possible to employ only asingle powder source, or more than two sources. Powder sources 50 and 51are connected, respectively, to conduits 52 and 53 which extend throughthe handle portion of casing 10 to passages or ports 54 and 55 (FIGURE3) in front electrode 18. Passages 54 and 55 communicate with nozzlepassage 25 at points which lie generally in a single plane perpendicularto the axis of passage 25. Such plane is spaced a short distance fromthe forward radial surface of electrode 18, the distance beinginsufiicient to result in deposition of spray material in the outer orforward end of passage 25. The passages 54 and 55, at least at theirpoints adjacent passage 25, are substantially radial to the axisthereof.

Each of the powder sources 50 and 51 includes a suitable source ofpropellant gas, and means to mix such gas with the powder, so that thepowder is propelled by the gas through the associated conduit and intonozzle passage 25. Thus, for example, the propellant gas in each sourcemay be introduced into a chamber containing spray powder, so that aportion of the powder becomes entrained in the gas and is carriedthereby to the nozzle passage.-

The remaining component of the torch comprises a spark plug element 57which is threaded or force-fit into phenolic body 13, being illustratedas inclined toward the inner surface of nozzle electrode 18. A look nut58 is threaded over the outer portion of spark plug 57 and is adapted tomaintain the same in the desired adjusted position. The spark plugcooperates with front electrode 18 in generating a spark in vortexchamber 26, so that the gas therein becomes ionized and may be employedto initiate an are between electrode rod 30 and the wall of nozzlepassage 25.

Method of spraying plastics in accordance with the present invention Themethod is performed by initiating and maintaining the electric are 26 inthe nozzle passage 25, while intro- 4 ducing gas from source 46 so thatthe plasma jet 12 is created. The various parameters are so regulatedthat the particular plastic or plastics to be introduced throughpassages 54 and 55 will be melted, but not decomposed or adverselyaffected in any way, by the heat of jet 12.

More specifically, the back electrode 30 is moved rearwardlysufiiciently far that the downstream footpoint thereof is located asubstantial distance upstream from the passages 54 and 55. Thus, theentire arc 26 is spaced substantially upstream from the point or pointsof materials introduction, 50 that the plastic is not deteriorated bythe intense heat of the arc.

The rate of flow of gas from source 46, and the electrical powersupplied to the are, are also regulated to such values that the plasticsubstance or substances will not disintegrate but instead merely melt.Thus, the electrical power may be relatively low, and the gas flow raterelatively high.

The plastic powder is introduced, by means of a suitable propellant gas,from sources 50 and 51 into passages 54 and 55 and thence into theplasma jet 12. The powder is melted by the jet 12 and impinged againstthe substrate S. It then cools and solidifies on the substrate, so thata coating is formed thereon.

The plastic substance may comprise, for example, an epoxy resincontaining a suit-able catalyst as in the fluidized bed process. Theplastic may also comprise polyethylene, nylon, and numerous others.

The gas introduced from source 46 may comprise argon, nitrogen, orvarious others. The same or other gases may be employed to propel theplastic powder from sources 50 and 51.

As one specific example of the present method, let it be assumed that itis desired to spray an epoxy resin onto the substrate S. The powersupplied to the arc may be amperes at 35 volts.

The rate of flow of propellant gas is 0.3 c.f.m. in each of the systems,both of which contain epoxy powder of the type employed in fluidized bedtechniques. Such powder incorporates (in powder form) a catalyst orhardener which melts and becomes active at a temperature lower than thatof the plasma jet 12. The rate of arc gas flow lthrough passage 48) maybe 1.3 c.f.m. Very importantly, the electrode 30 is disposed in aretracted position, so that the downstream arc footpoint is (unlike thefootpoint position shown in the drawing) spaced upstream from the planeof passages 54 and 55. This spacing may be approximately one-half inch.When the epoxy-catalyst powder enters the jet 12, it melts andsubsequently hardens on substrate S.

The present invention, and all of the appended claims, are to beconstrued as limited to plastics which, upon an increase in temperature,melt before they deteriorate. Thus, for example, a plastic which burnswhile still in solid form is not within the scope of any claim.

Various embodiments of the present invention, in addition to what hasbeen illustrated and described in detail, may be employed withoutdeparting from the scope of the accompanying claims.

We claim:

1. A method of applying a plastic onto a substrate, which comprisesproviding an electrical plasma-jet torch having a nozzle passage,supplying gas and electrictiy to said torch and generating an electricarc therein with consequent formation of a plasma jet which emanatesfrom said nozzle passage, directing said jet toward a substrate which itis desired to coat with a plastic, providing a plastic, regulating theparameters of said torch in such manner that the region of said nozzlepassage which is relatively adjacent said substrate does not contain anyportion of said electric arc and is at a temperature insufiicientlyhighto effect deterioration of said plastic but sutficiently high tomelt the same, and introducing said plastic into said nozzle passage atsaid region thereof which is relatively adjacent said substrate wherebysaid plastic is melted therein and entrained in said jet for impingementagainst said substrate, said plastic then solidifying on said substrateto form a coating thereon.

2. The invention as claimed in claim 1, in which said plastic isprovided in powder form.

3. The invention as claimed in claim 1, in which said plastic is apowdered epoxy resin containing therein a catalyst in powder form.

6 References Cited UNITED STATES PATENTS 3,090,696 5/1963 Gemrner 117-213,179,734 4/1965 Johnson 117--93.4 3,183,337 5/1965 Winzler et al. 21976ALFRED L. LEAVITT, Primary Examiner. RICHARD D. NEVIUS, Examiner.

10 A. GOLIAN, Assistant Examiner.

1. A METHOD OF APPLYING A PLASTIC ONTO A SUBSTRATE, WHICH COMPRISESPROVIDING AN ELECTRICAL PLASMA-JET TORCH HAVING A NOZZLE PASSAGE,SUPPLYING GAS AND ELECTRICITY TO SAID TORCH AND GENERATING AN ELECTRICARC THEREIN WITH CONSEQUENT FORMATION OF A PLASMA JET WHICH EMANATESFROM SAID NOZZLE PASSAGE, DIRECTING SAID JET TOWARD A SUBSTRATE WHICH ITIS DESIRED TO CAOT WITH A PLASTIC, PROVIDING A PLASTIC, REGULATING THEPARAMETERS OF SAID TORCH IN SUCH MANNER THAT THE REGION OF SAID NOZZLEPASSAGE WHICH IS RELATIVELY ADJACENT SAID SUBSTRATE DOES NOT CONTAIN ANYPORTION OF SAID ELECTRIC ARE AND IS AT A TEMPERATURE INSUFFICIENTLYHIGHTO EFFECT DETERIORATION OF SAID PLASTIC BUT SUFFICIENTLY HIGH TOMELT THE SAME, AND INTRODUCING SAID PLASTIC INTO SAID NOZZLE PASSAGE ATSAID REGION THEREOF WHICH IS RELATIVELY ADJACENT SAID SUBSTRATE WHEREBYSAID PLASTIC IS MELTED THEREIN AND ENTRAINED IN SAID JET FOR IMPINGEMENTAGAINST SAID SUBSTRATE, SAID PLASTIC THEN SOLIDIFYING ON SAID SUBSTRATETO FORM A COATING THEREON.